Pneumatic tire having pitch sequencing

ABSTRACT

The present invention relates to a pneumatic tire having a tread with a plurality of load-supporting elements placed above the circumference of the tire. The tread is characterized by a pitch sequence comprising 
     (a) from 52 to 64 total pitches; 
     (b) only four different pitch lengths and the lowest indivisible integers used for the pitch ratios for the four pitch lengths are 11-13-15 and 17; 
     (c) a ratio of the longest pitch to the shortest pitch length ranging from 1.54 to 1.55; 
     (d) there being a constant increment in pitch length in the four different pitch lengths as one progresses from the shortest pitch length to the longest pitch length.

BACKGROUND OF THE INVENTION

The present invention relates to a pneumatic tire, more particularly toa tread pattern for pneumatic tire.

As a tire travels upon a surface, there occurs a movement of air,creating an audible sound. For any given tread pattern, a certain amountof acoustic energy is produced. While two different tread patterns mayproduce the same amount of acoustic energy, the noise produced by eachmay have dramatically different effects on people. One tire may soundharsh and disagreeable and the other quite acceptable. The differencebetween the two sounds is in their frequency spectrum and may result ina different subjective audible reaction. The condition where the soundgenerated is dominated by a single frequency and its harmonics, i.e., amajority of the sound generated being concentrated into very smallfrequency range of the sound spectrum is undesirable. This situation ispsychologically upsetting to a listener, creating an uneasy feeling.Additionally, besides being irritating, total sounds can be perceived atgreater distances and require more sound-proofing material than donon-total sounds. If a given concentration of sound energy could bespread out over a wider range of frequency, it would reduce the enologyor the undesirability of the sound.

Various methods have been suggested in the past to reduce objectionablenoise generated by tires by spreading the energy produced over thefrequency range. For example, U.S. Pat. Nos. 4,327,792 and 4,474,223disclose a method of spreading noise by load-supporting elements of atire tread. This is accomplished by designing load-bearing elements inaccordance with a five-step procedure to determine the maximum number ofrepeating design cycles which may be used, selecting the maximum pitchratio, determining the appropriate number of harmonic segments intowhich the tread can be divided, determining the size of each harmonicsegment and the number of design cycles for each harmonic segment andlastly arranging the various design cycles in each of the harmonicsegments so that the wave length of the predominant modulation frequencyof the segment corresponds to the formula length of that segment.

SUMMARY OF THE INVENTION

The present invention relates to a tire provided with a tread having aplurality of load-supporting elements placed above the circumference ofthe tire. The tread has a pitch sequence comprising:

(a) from 52 to 64 total pitches;

(b) only four different pitch lengths and the lowest indivisibleintegers used for the pitch ratios for the four pitch lengths are11-13-15 and 17;

(c) a ratio of the longest pitch length to the shortest pitch lengthranging from 1.54 to 1.55; and

(d) there being a constant increment in pitch length in the fourdifferent pitch lengths as one progresses from the shortest pitch lengthto the longest pitch length.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphical illustration of the Harmonic Analysis of theImpulse function for a tire tread having 52 pitches made in accordancewith the present invention and using the pitch sequence disclosedherein.

FIG. 2 is a graphical illustration of the Harmonic Analysis of theImpulse function for a tire tread having 52 pitches and made inaccordance with U.S. Pat. No. 4,474,223.

FIG. 3 is a graphical illustration of the Harmonic Analysis of theImpulse function for a tire tread having 64 pitches made in accordancewith the present invention and using the pitch sequence disclosedherein.

FIG. 4 is a graphical illustration of the Harmonic Analysis of theImpulse function for a tire tread having 64 pitches and made inaccordance with U.S. Pat. No. 4,474,223.

DETAILED DESCRIPTION OF THE INVENTION

As used herein and in the claims, the following terms are intended tomean:

"Pitch" also known as "design cycle" means a section of the tread in thecircumferential direction which is repeated around the outercircumference of the tire. Normally, a pitch contains a load-bearingelement and an adjacent groove which separates adjoining load-bearingelements in a tire tread. However, the boundaries of a pitch in thecircumferential direction may bisect a load-bearing element or adjacentgroove, depending on the point on the boundary in the axial direction.Even so, each pitch generally contains the total of at least oneload-bearing element and at least one groove, but it may consist of twofractions which total one complete element or groove.

"Pitch ratio" means the ratio of the longest design cycle length to theshortest design cycle length.

"Pitch sequence" means the particular arrangement of different designcycle length segments around the full circumference of the tread.

"Pneumatic tire" means a laminated mechanical device of generallytoroidal shape (usually an open torus) having beads, a carcass ply and atread.

The pneumatic tires of the present invention have improved pitchsequencing. Use of these sequences in tires result in improvedsubjective noise properties.

The ratio of the longest pitch length to the shortest pitch lengthranges from 1.54 to 1.55. Preferably, the ratio is 1.545.

In the pitch sequences used in the present invention, the lowestindivisible integers used for pitch ratios for the four pitch lengthsare 11, 13, 15 and 17. There is a constant increment in pitch length inthe four different pitch lengths as one progresses from the shortestpitch length to the longest pitch length. For example, for the pitchlength ratio, 11, 13, 15, 17, then is a constant increment of 2.

There are five pitch sequences which are preferred embodiments of thepresent invention. In terms of this pitch ratios, the following sequenceare disclosed. The sequences below are interpreted in terms of a closedloop (like a tire) and any pitch can initiate the sequence or terminatethe sequence so long as the order of the sequence is maintained.

The first pitch sequence consists of 52 total pitches. The pitchsequence is as follows:

    ______________________________________                                        11   13      15     17   17   15   15   11   13   11                          11   11      13     15   17   15   11   11   13   11                          15   13      17     17   15   13   11   13   17   13                          13   15      15     15   13   13   11   11   13   15                          13   13      17     15   11   13   11   15   17   11                          11    11.                                                                     ______________________________________                                    

The second preferred pitch sequence has a total of 57 pitches and is asfollows:

    ______________________________________                                        13   13     13     13   11   15   11    17   13   15                          13   17     15     17   15   13   11    13   11   11                          13   15     15     13   11   11   13    13   17   15                          15   13     17     13   13   11   11    11   11   11                          13   15     17     15   13   15   11    11   11   11                          11   13     13     15   17   15    11.                                        ______________________________________                                    

The third preferred pitch sequence consists of 59 total pitches and isas follows:

    ______________________________________                                        15   17     17     13   15   11   13   11    11   13                          15   15     17     13   15   13   11   15    11   15                          13   13     11     11   11   15   17   15    11   11                          13   15     13     11   11   11   11   11    15   15                          13   17     13     13   11   11   11   13    15   17                          11   13     11     17   15   15   11   13     13.                             ______________________________________                                    

The fourth preferred pitch sequence consists of 62 total pitches and isas follows:

    ______________________________________                                        11   11      13     15   15   17   17   15   11   13                          13   11      17     13   15   11   13   15   17   17                          15   13      11     11   11   13   13   15   17   15                          15   15      13     15   11   11   13   15   17   15                          13   11      11     13   13   15   13   11   11   13                          15   17      13     11   13   15   15   17   13   13                          11    11.                                                                     ______________________________________                                    

The fifth preferred pitch sequence consists of 64 total pitches and isas follows:

    ______________________________________                                        15   13     15     11    13   11   15   17   15   13                          15   15     15     17    11   13   11   11   11   11                          13   15     17     15    15   11   11   11   13   13                          15   17     15     13    15   13   17   15   15   17                          15   15     11     13    13   11   13   15   17   17                          15   13     15     13    11   15   15   13   17   13                          13   13     11      13.                                                       ______________________________________                                    

The tires of the present invention may be for passenger vehicles,multi-purpose vehicles, light truck and medium truck.

According to the present invention, what determines the individualdesign cycles length on a given tire are the requirements of (a) therebeing only from 52 to 64 total pitches, (b) only four different pitchlengths, (c) the specific pitch sequence, (d) the four design cyclelength ratios and (e) the known outer circumference of the tire. Todetermine how long each design cycle would be for a tire of a givenouter circumference, one takes the sum of all the integers in the pitchsequence expressed in terms of ratios. For example, for the above 52pitch sequence, the sum would be 702 (11×16+13×15+15×13+17×8). For atire of the size P195/64R15, the outer circumference would be 2001 mm.If one divides the outer circumference 2001 mm by 702, one gets 2.85.One takes this number 2.85 and multiplies it by 11, 13, 15 and 17 toyield the respective pitch lengths, 31.35 mm, 37.05 mm, 42.75 mm and48.45 mm.

EXAMPLE 1

Computer simulation tests have been performed comparing the HarmonicAnalysis of the Impulse function of tire treads with pitch sequencesarranged according to the present invention versus pitch sequencesaccording to U.S. Pat. No. 4,474,223.

FIG. 1 is a graphical illustration of the Harmonic Analysis of theImpulse function using the pitch sequence consisting of 52 individualpitches which are as follows:

    ______________________________________                                        11   13      15     17   17   15   15   11   13   11                          11   11      13     15   17   15   11   11   13   11                          15   13      17     17   15   13   11   13   17   13                          13   15      15     15   13   13   11   11   13   15                          13   13      17     15   11   13   11   15   17   11                          11    11.                                                                     ______________________________________                                    

FIG. 2 is a graphical illustration of the Harmonic analysis of theImpulse function using a pitch sequence consisting of 52 individualpitches in accordance with U.S. Pat. No. 4,474,223 and which are asfollows:

    ______________________________________                                        7    7      7      7    7    9     9    9    9    9                           11   11     11     11   11   9     9    9    7    7                           7    7      9      9    9    9     11   11   11   11                          9    7      7      7    9    9     9    11   11   11                          9    7      7      7    9    9     9    11   11   11                          9     9.                                                                      ______________________________________                                    

In comparing the FIGS. 1 and 2, it is seen that the Fourier spectrum ofthe impulse function for the tire tread where the pitch sequence isarranged according to the current invention (FIG. 1) has flatterharmonics components than the pitch sequence in FIG. 2. The flatterharmonics components translate to reduced tire noise as the tirecontacts the road surface. The quality of the calculated Fourierspectrum can be also expressed by a maximum Normalized Amplitude. It isclearly visible from comparison of FIGS. 1 versus 2 that the maximumNormalized Amplitude calculated from pitch sequence(s) arrangedaccording to the present invention are lower that those arranged inaccordance to the U.S. Pat. No. 4,474,223. Accordingly, it has beendetermined that a tire having pitches arranged according to the currentinvention has a reduction in tread noise as the tire contacts the roadsurface. In particular, there is a reduction of the maximum amplitude in200 harmonic spectrum by more than 20 percent.

EXAMPLE 2

Computer simulation tests have been performed comparing the HarmonicAnalysis of the Impulse function of tire treads with pitch sequencesarranged according to the present invention versus pitch sequencesaccording to U.S. Pat. No. 4,474,223.

FIG. 1 is a graphical illustration of the Harmonic Analysis of theImpulse function using the pitch sequence consisting of 64 individualpitches which are as follows:

    ______________________________________                                        15   13     15     11    13   11   15   17   15   13                          15   15     15     17    11   13   11   11   11   11                          13   15     17     15    15   11   11   11   13   13                          15   17     15     13    15   13   17   15   15   17                          15   15     11     13    13   11   13   15   17   17                          15   13     15     13    11   15   15   13   17   13                          13   13     11      13.                                                       ______________________________________                                    

FIG. 4 is a graphical illustration of the Harmonic analysis of theImpulse function using a pitch sequence consisting of 64 individualpitches in accordance with U.S. Pat. No. 4,474,223, and which are asfollows:

    ______________________________________                                        7    7      7      7     9    9    9    9    11   11                          11   11     9      9     7    7    9    9    11   11                          9    9      9      7     9    11   9    9    9    7                           7    7      9      9     9    11   11   11   9    9                           9    7      7      9     9    11   11   9    9    9                           7    9      11     9     9    9    7    7    9    9                           11   11     9       9.                                                        ______________________________________                                    

In comparing the FIGS. 3 and 4, it is seen that the Fourier spectrum ofthe impulse function for the tire tread where the pitch sequence isarranged according to the current invention (FIG. 3) has flatterharmonics components than the pitch sequence in FIG. 4. The flatterharmonics components translate to reduced tire noise as the tirecontacts the road surface. The quality of the calculated Fourierspectrum can be also expressed by a maximum Normalized Amplitude. It isclearly visible from comparison of FIGS. 3 versus 4 that the maximumNormalized Amplitude calculated from pitch sequence(s) arrangedaccording to the present invention are lower that those arranged inaccordance to the U.S. Pat. No. 4,474,223. Accordingly, it has beendetermined that a tire having pitches arranged according to the currentinvention has a reduction in tread noise as the tire contacts the roadsurface. In particular, there is a reduction of the maximum amplitude in200 harmonic spectrum by more than 30 percent.

What is claimed is:
 1. A tire provided with a tread having a pluralityof load-supporting elements placed about the circumference of said tire,said tread having a pitch sequence comprising:(a) 52, 57, 59, 62 or 64total pitches; (b) only four different pitch lengths and the lowestindivisible integers used for the pitch ratios for the four pitchlengths are 11-13-15 and 17; (c) a ratio of the longest pitch length tothe shortest pitch length ranging from 1.54 to 1.55; and (d) there beinga constant increment in pitch length in the four different pitch lengthsas one progresses from the shortest pitch length to the longest pitchlength; wherein said 52 total pitches consist of

    ______________________________________                                        11   13     15     17   17   15   15   11   13   11                           11   11     13     15   17   15   11   11   13   11                           15   13     17     17   15   13   11   13   17   13                           13   15     15     15   13   13   11   11   13   15                           13   13     17     15   11   13   11   15   17   11                           11    11;                                                                     ______________________________________                                    

wherein said 57 total pitches consist of

    ______________________________________                                        13   13     13     13   11   15   11   17   13   15                           13   17     15     17   15   13   11   13   11   11                           13   15     15     13   11   11   13   13   17   15                           15   13     17     13   13   11   11   11   11   11                           13   15     17     15   13   15   11   11   11   11                           11   13     13     15   17   15    11;                                        ______________________________________                                    

wherein said 59 total pitches consist of

    ______________________________________                                        15   17     17     13   15   11   13   11   11   13                           15   15     17     13   15   13   11   15   11   15                           13   13     11     11   11   15   17   15   11   11                           13   15     13     11   11   11   11   11   15   15                           13   17     13     13   11   11   11   13   15   17                           11   13     11     17   15   15   11   13    13;                              ______________________________________                                    

wherein said 62 total pitches consist of

    ______________________________________                                        11   11     13     15   15   17   17   15   11   13                           13   11     17     13   15   11   13   15   17   17                           15   13     11     11   11   13   13   15   17   15                           15   15     13     15   11   11   13   15   17   15                           13   11     11     13   13   15   13   11   11   13                           15   17     13     11   13   15   15   17   13   13                           11    11;   and                                                               ______________________________________                                    

wherein said 64 total pitches consist of

    ______________________________________                                        15   13     15     11   13   11   15   17   15   13                           15   15     15     17   11   13   11   11   11   11                           13   15     17     15   15   11   11   11   13   13                           15   17     15     13   15   13   17   15   15   17                           15   15     11     13   13   11   13   15   17   17                           15   13     15     13   11   15   15   13   17   13                           13   13     11     
 13.                                                       ______________________________________                                    


2. The tire of claim 1 wherein the pitch sequence consists of 52 totalpitches and consisting of

    ______________________________________                                        11   13     15     17    17   15   15   11   13   11                          11   11     13     15    17   15   11   11   13   11                          15   13     17     17    15   13   11   13   17   13                          13   15     15     15    13   13   11   11   13   15                          13   13     17     15    11   13   11   15   17   11                          11   
 11.                                                                     ______________________________________                                    


3. The tire of claim 1 wherein the pitch sequence consists of 57 totalpitches and consisting of

    ______________________________________                                        13   13     13     13    11   15   11   17   13   15                          13   17     15     17    15   13   11   13   11   11                          13   15     15     13    11   11   13   13   17   15                          15   13     17     13    13   11   11   11   11   11                          13   15     17     15    13   15   11   11   11   11                          11   13     13     15    17   15   
 11.                                       ______________________________________                                    


4. The tire of claim 1 wherein the pitch sequence consists of 59 totalpitches and consisting of

    ______________________________________                                        15   17     17     13    15   11   13   11   11   13                          15   15     17     13    15   13   11   15   11   15                          13   13     11     11    11   15   17   15   11   11                          13   15     13     11    11   11   11   11   15   15                          13   17     13     13    11   11   11   13   15   17                          11   13     11     17    15   15   11   13   
 13.                             ______________________________________                                    


5. The tire of claim 1 wherein the pitch sequence consists of 62 totalpitches and consisting of

    ______________________________________                                        11   11     13     15    15   17   17   15   11   13                          13   11     17     13    15   11   13   15   17   17                          15   13     11     11    11   13   13   15   17   15                          15   15     13     15    11   11   13   15   17   15                          13   11     11     13    13   15   13   11   11   13                          15   17     13     11    13   15   15   17   13   13                          11   
 11.                                                                     ______________________________________                                    


6. The tire of claim 1 wherein the pitch sequence consists of 64 totalpitches and consisting of

    ______________________________________                                        15   13     15     11    13   11   15   17   15   13                          15   15     15     17    11   13   11   11   11   11                          13   15     17     15    15   11   11   11   13   13                          15   17     15     13    15   13   17   15   15   17                          15   15     11     13    13   11   13   15   17   17                          15   13     15     13    11   15   15   13   17   13                          13   13     11     
 13.                                                       ______________________________________                                    


7. The tire of claim 1 wherein said tire is a passenger tire.
 8. Thetire of claim 1 wherein said tire is a light truck tire.
 9. The tire ofclaim 1 wherein said tire is a medium truck tire.